Many computing systems such as portable calculators and portable computers require an internal battery in order to operate independent from AC lines. The eventual discharge of the internal battery can cause problems for a computer system operator if sufficient warning of power loss is not given.
Traditionally, battery powered computer systems have only provided the user with a low battery indicator which informs the user when the voltage level of the battery falls below a predetermined value. This provides a warning to the user of imminent power loss, but does not allow for longer range anticipation of power loss.
Another method for monitoring battery discharge is for the user to set a timer immediately upon charging the battery. By referencing the timer the user can determine how long the computing system has been running since the battery was last recharged. This method unfortunately has many drawbacks. For instance, the user must intervene to reset the timer each time the battery is recharged. Failure to set the timer or improper setting of the timer results in inaccurate predictions of the time of power loss. Additionally, if an operator only partially charges the battery, he has no way of knowing how much charge has been placed in the battery, and therefore no reference point from which to estimate the time of power loss. Furthermore, this method does not take into account that some operations in a computing system consume more power than other operations. Failure to take this into account again results in inaccurate predictions of the time of power loss.